Fiber circuits open several new methods of building systems for optical networks. These applications take advantage of the unique abilities of the circuits to control the position, length, and shape of a large collections of fibers. In all situations, the functions provided by the circuits are not readily realizable through any other known method of construction and illustrate the high value added by a fundamentally simple element. In the future, we anticipate many situations where the control of fiber properties is critical not only as an efficient manufacturing method, but also as an element of the product operation.